The present invention relates to a plasma processing apparatus that processes a surface of a substrate-like sample, such as a semiconductor wafer, located or disposed in a vacuum container using plasma during a semiconductor device manufacturing process and more particularly to a plasma processing apparatus that performs processing by adjusting a temperature of a sample stand or sample table (or stage) used to hold the sample in a lower part of a process chamber in the vacuum container.
In such a plasma processing apparatus, in improving the accuracy of processing on the surface of the semiconductor wafer, the sample to be processed, it is important to suppress temperature variations of the surface of the wafer being processed and keep it uniform over the entire surface. Further, by properly adjusting the temperature of the wafer surface in each step of processing a plurality of films formed stacked one upon the other on the semiconductor wafer surface, the processing accuracy, selection ratio and throughput can be improved.
However, as semiconductor wafers increase in diameter and surface area in recent years, an electric power that the plasma processing apparatus applies to the semiconductor wafers during processing tends to increase. Particularly in a process of etching an insulating film, a large electric power on the order of kilowatt is applied in order to improve an etch rate. The application of such a large electric power results in an increase in an energy of impact with the semiconductor wafer produced by ions when attracted to the surface of the semiconductor wafer during the processing, which in turn increases the amount of heat the semiconductor wafer receives. Under these circumstances, there is a growing demand for a technology to adjust the temperature of the wafer stably, at high speed and with high precision.
In the plasma processing apparatus, it has been a conventional technique to adjust the temperature of a surface of a specimen holding stand that contacts a back of the specimen in order to control the surface temperature of the specimen, such as semiconductor wafer. That is, a technology has been adopted that adjusts the temperatures of the interior and surface of the sample table by a temperature adjusting means disposed inside the sample table.
The temperature adjusting method, for example, involves forming a coolant path in the specimen stand and flowing the coolant in the path to exchange heat between the coolant and the members inside the sample table and thereby keep the surface temperature of the sample table within a predetermined range. Such a coolant is circulated through a passage connecting a coolant supply device (for example, chiller unit) and the path inside the sample table and is adjusted to a predetermined temperature by a cooling device or heating device in the coolant supply device and supplied to the path in the sample table for heat exchange before being returned to the coolant supply device.
This coolant supply device is constructed to temporarily store the coolant in a tank in which the coolant is adjusted in temperature and then to supply the temperature-adjusted coolant to the sample table. With this technology, since the coolant has a large heat capacity compared with an increase or decrease in heat applied to the specimen, the surface temperature of the specimen can be kept constant effectively even when there are some variations in heat received by the specimen. On the other hand, since the temperature of the coolant greatly affects the temperature of the sample table and therefore the specimen, the variation in the coolant temperature has a large influence on the temperature change of the specimen. That is, a coolant with so large a heat capacity that its temperature change is small has difficulty coping with and adjusting rapid temperature changes of the specimen. Further, since its heat efficiency is low, the amount of coolant needs to be increased to cope with an increased quantity of heat received, making it necessary to increase the size of the coolant supply device, which in turn increases the manufacturing and installation cost of the plasma processing apparatus.
In contrast with such a conventional technology, a method for adjusting the temperature of the sample table using a so-called direct expansion type coolant supply device is being proposed. This type of coolant supply device has a coolant compressor, condenser and expander disposed in the passage in which the coolant circulates, in order to make the coolant circulation passage function as a refrigeration cycle so as to cool the sample table by evaporating the coolant in the path within the sample table so that the sample table can work as an evaporator in the refrigeration cycle. Known examples of such a technology are disclosed in JP-A-6-346256 and JP-A-2005-83864.